For a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor or CCD (Charge Coupled Device) image sensor, and other image input sensors, since their characteristics have improved, the demand for them in of digital camera applications and camera-equipped cell phone applications has been increasing. For said image sensors, there is a demand for further improvement of characteristics, such as expansion of the dynamic range.
For example, Japanese Kokai Patent Application No. 2003-134396, Japanese Kokai Patent Application No. 2000-165754, Japanese Kokai Patent Application No. 2002-77737, and Japanese Kokai Patent Application No. Hei 5[1993]-90556 disclose solid-state image pickup devices that realize a wider dynamic range. However, for these solid-state image pickup devices, it is difficult to realize a wider dynamic range while maintaining high sensitivity and a high S/N ratio. In order to solve this problem, Japanese Kokai Patent Application No. 2005-328493 discloses a type of solid-state image pickup device.
For the solid-state image pickup device described in Japanese Kokai Patent Application No. 2005-328493, the structure is such that the photoelectric charge overflowing from the photodiode of each pixel is accumulated in the floating diffusion and an electrostatic capacitive element. The signal of each pixel is obtained by the photoelectrons in the diode when the photoelectrons do not overflow, or by both photoelectrons in the photodiode and photoelectrons overflowing from the photodiode when said photoelectrons overflow from the photodiode.
However, for the solid-state image pickup device described in Japanese Kokai Patent Application No. 2005-328493, when it is manufactured in a CMOS process, the dark current component than the photoelectrons overflowing from the photodiode becomes larger, e.g., by 3-4 orders of magnitude, than the desired level. This is undesired for use in accumulating photoelectric charge over a long time, and there is a demand for suppression of this phenomenon.
Sites for generation of the dark current component include the interface just below the gate of the transistor, the side surface of the element-separating insulating film, the portion in contact with the depletion layer on the silicon surface, etc.
A problem to be addressed is the difficulty in suppressing the dark current component than the photoelectrons overflowing from the photodiode in a solid-state image pickup device with a wide dynamic range.